Question

What is the penalty for illegally claiming someone as a dependent?.

Answer 1

Civil Penalties
If the IRS concludes that you knowingly claimed a false dependent, they can assess a civil penalty of 20% of your understood tax Failing to be honest by claiming a false dependent could result in 3 years of prison and fines up to $250,000.

Answer 2

you can ask them to give an amended return to fix the problem